(1) Field of the Invention
The present invention relates to a deposition head for depositing an impregnated fiber tape, and to a device for placing such a tape. The invention is thus situated in the technical field of fabricating parts out of composite materials by using the fiber placement method to place an impregnated fiber tape.
(2) Description of Related Art
The fiber placement method is a method that is an alternative to winding a continuous filament.
Fiber placement is a method of depositing fibers, tapes, roving, or other similar kinds of reinforcement, whether dry or preimpregnated with resin, onto surfaces of various shapes. Such placement is performed by using a device having a movable deposition head. The deposition head thus serves to position the material used on a surface by direct mechanical contact with that surface. For this purpose, the deposition head is driven by a drive system such as a robot arm or a positioning gantry, having its degrees of freedom servo-controlled to match the shape of the surface of the body for covering.
The fiber placement method thus serves in particular to make surfaces of large dimensions and small thicknesses, within the limits of the size of the deposition head.
In particular, the fiber placement method makes it possible to perform tape deposition sequences automatically. Each sequence includes operations of approaching, deposition, and cutting.
Placing a fiber tape on a part by means of a placement device can be difficult. Specifically, the material in tape form that is deposited by a placement device tends to be tacky.
It should be recalled that tack is a state of a “sticky” surface, i.e. a surface that has the property of adhering to itself or to some other body merely by making contact. In particular, a fiber tape impregnated with a matrix may be impregnated by a wet technique. By way of example, this impregnation technique consists in impregnating carbon or glass or indeed basalt fibers by dipping them in a resin in the liquid state.
Another technique consists in diluting a viscous resin in a solvent and then in evaporating the solvent after impregnating the fibers. This technique is referred to as the solvent technique or impregnation by dissolving.
At ambient temperature, tapes having fibers that have previously been impregnated by the wet technique generally present tack that is higher than the tack of tapes that have previously been impregnated by the solvent technique. Such low tack of tapes of fibers that have previously been impregnated by the solvent technique is associated with greater stiffness that also provides the fiber tape with greater stability. The fiber tape is thus less “sticky” and more “rigid” at ambient temperature than a tape of fibers impregnated by the wet technique.
Fiber tapes presenting high tack tend to adhere to the guide, peeling, and drive surfaces of placement devices, and indeed tend to clog such placement devices.
Thus, the fiber tapes used for making parts by fiber placement are advantageously impregnated using the solvent technique, since such fiber tapes impregnated by the solvent technique are easier to convey and to guide, and they make it easier to superpose plies on one another. Such fiber tapes impregnated by the solvent technique also limit the transfer of resin onto the placement device, thereby serving to reduce the risk of breakdown by clogging and to reduce the operations needed for cleaning the placement device.
In contrast, such fiber tapes impregnated by the solvent technique are available on the market at costs that are significantly higher than fiber tapes impregnated by the wet technique.
Furthermore, a fiber placement sequence comprises in succession an approach stage, a deposition stage, and a cutting stage.
During the approach stage, the fiber tape is taken towards the deposition surface. During the deposition stage, the fiber tape is deposited on the deposition surface. Finally, during the cutting stage, the fiber tape is cut.
A deposition head thus usually includes a cutter system. By way of example, a cutter system may be constituted by a pneumatic guillotine driving a metal blade in order to cut the fiber tape. Because of the size of the cutter system, a considerable transition distance lies between the plane in which the fiber tape is cut and the plane where the fiber tape is deposited on the deposition surface. During the approach stage, the fiber tape thus needs to be moved along this transition distance, which can be difficult, in particular with fiber tapes that have been impregnated by the wet technique and that are floppy.
Document WO 01/96223 describes a deposition head for depositing tows of fibers arranged on a storage spool. The deposition head includes a motor-driven wheel driving fiber tows towards compacting means via guide rollers. At the outlet from the compacting means, the fiber tows are directed towards a deposition roller. Cutter means are interposed between the compacting means and the deposition roller.
Document GB 2 492 594 describes a deposition head. That deposition head comprises a first storage spool having wound thereon a backing tape with resin adhered thereto. The deposition head has a second storage spool with a fiber tape wound thereon. The fiber tape comes into contact with the resin and the backing tape on passing through a device comprising a heater roller and an adhesion roller. Under such circumstances, the assemblage comprising the backing tape, the fiber tape, and the resin passes between a deposition roller and a peeling shoe. The backing tape passes around the peeling shoe in order to be separated from the resin, while, on the contrary, the resin together with the fiber tape are deposited on the deposition surface. A compression shoe then compresses the fiber tape and the resin against the deposition surface.
That solution makes use of a backing tape. In general manner, it can be difficult to peel off a backing tape. Specifically, fibers of the fiber tape can remain attached to the backing tape under certain conditions.
Document U.S. Pat. No. 5,110,395 describes a fiber deposition head for a fiber placement machine. Tows that are individually impregnated with resin and referred to as “towpregs” are brought at independent speeds from a creel assembly in order to apply fiber bands on a deposition surface.
The deposition head includes an applicator in the form of a shoe or a roller for applying the tape against the deposition surface.
Documents U.S. Pat. No. 6,540,000 and FR 2 785 623 disclose a device having spools containing tapes. The tapes are brought together by deflector pulleys so as to form a sheet made up of a plurality of juxtaposed tapes that pass through brake means in order to reach a deposition roller. The break means comprise two jaws driven by an actuator, with the sheet traveling between the two jaws.
The deflector pulleys, the break means, and the deposition roller are arranged on a plate that can be moved in elevation.
The plate also carries a blade suitable for rotating in order to cut the sheet against an ultrasonically vibrating anvil of the deposition head.
The deposition head does not make use of a backing tape that ends up needing to be peeled off.
Document FR 2 982 792 describes a deposition head for depositing a tape of impregnated fibers that is provided with a spool carrying an assemblage of tapes including the tape of impregnated fibers arranged on a separator tape. The deposition head includes a spool for recovering the separator tape together with parting means for parting the tape of impregnated fibers from the separator tape. The deposition head includes a smoother having a sharp or rounded edge and arranged after the parting means in the travel direction of the tape of impregnated fibers, the tape of impregnated fibers coming into contact solely with said edge.
Documents U.S. Pat. No. 5,480,508, DE 10 2012 017595, WO 2015/068734, and EP 0 144 927 are also known.
Document U.S. Pat. No. 5,480,508 discloses a deposition head having a vertically movable peeling roller.